Atticus is a realist rather than an idealist. What does this mean?

Atticus knows that an institution is only as good as the people who serve it. He's not foolish enough to believe the court systems are perfect, but he hopes the men chosen to serve will do their duty with clear heads. Atticus also knows that there are certain biases that will keep people from doing the right thing...... because he's a realist. None-the-less, he believes in the system he serves.

I’m no idealist to believe firmly in the integrity of our courts and in the jury system—that is no ideal to me, it is a living, working reality. Gentlemen, a court is no better than each man of you sitting before me on this jury. A court is only as sound as its jury, and a jury is only as sound as the men who make it up. I am confident that you gentlemen will review without passion the evidence you have heard, come to a decision, and restore this defendant to his family. In the name of God, do your duty."